Edible oils containing lower levels of saturated fatty acids and elevated concentrations of oleic acids and poly unsaturated fatty acids such a linoleic acid are highly desirable due to the perceived dietary health benefits and possibly preventing diseases such as arteriosclerosis or diabetes. Moreover, monounsaturated oils, such as oleic acid are suitable replacements to petroleum-based feedstocks in the manufacture of plastic, lubricants and cosmetics and are known to enhance the combustion of biodiesel.
Vegetable oils extracted from plants comprise various amounts of saturated, mono- and polyunsaturated fatty acids and although mono- and polyunsaturated oils both have their use, polyunsaturated oils are considered contaminants in oils for industrial use as they are prone to oxidation and difficult to remove during oil processing. Therefore, plants with high concentrations of oleic acid (OA), a monounsaturated fatty acid, and low amounts of polyunsaturated fatty acids such as linoleic acid (LA) or alpha-linolenic acid (ALA) are highly desirable.
Two multifunctional classes of desaturases have been found in plants, one soluble and the other membrane bound. In plants C16- and C18-fatty acids are synthesized in the stroma of plastids and with desaturation of 18:0 to 18:1 by a soluble delta-9 stearoyl ACP desaturase also occurring in plastids. Further desaturation of fatty acids in membrane lipids of the chloroplast and endoplasmic reticulum (ER) is carried out by the membrane bound desaturases, a number of which have been designated FAD2 to FAD8.
The seeds of Cannabis sativa L. (hemp, marijuana) are an important source of oil and protein in human nutrition dating back to Neolithic times in ancient China. C. sativa has an annual life cycle and is mostly dioecious with male and female flowers borne on separate plants. Selective breeding has produced marijuana strains accumulating high levels of psychoactive cannabinoids in the female flowers and hemp cultivars typically having low levels of cannabinoids but good fibre and/or seed oil traits. Hemp has modest agrochemical requirements, is an excellent break crop and is suited to warm-to-temperate growing conditions. At over 80% in polyunsaturated fatty acids (PUFAs), hemp seed oil rivals most of the commonly used vegetable oils. At 56% LA and 22% ALA hemp oil is a rich source of these essential fatty acids. In addition, hemp oil also contains gamma linolenic acid (GLA) and stearidonic acid (SDA) which occur at about 4% and 2% respectively.
This disclosure relates to two novel desaturase genes in hemp catalysing desaturation of oleic acid (OA) to LA and LA to ALA. Homozygous plants lacking the delta-12 desaturase [also known as FAD2 desaturase] show increased amounts of OA, whereas plants lacking the delta-15 desaturase [also known as FAD3 desaturase] show increased amounts of LA and near zero levels of ALA. Plants carrying a specific point mutation in the delta-12 desaturase show increased amounts of GLA and when this delta-12 desaturase point mutation is crossed into plants lacking the delta-15 desaturase there is a further increase in the amounts of GLA, a profile desired to efficiently purify GLA from plants. Plants carrying single delta-12 desaturase or delta-15 desaturase mutations or both mutations are also disclosed, as are plants engineered to down-regulate or ablate expression of delta-12 desaturase and/or delta-15 desaturase.